JPH06264160A - Composite ceramic tube - Google Patents

Abstract

PURPOSE:To enhance the creep strength, oxidation resistance and thermal impact property of radiant tubes, etc., by improving the high-temp. characteristics of these tubes so that a high-temp. furnace operation for enhancing the efficiency of the furnace operation is made possible and that the accuracy of furnace temp. control is improved. CONSTITUTION:This tube is formed of Si as a matrix and has a composite structure contg. SiC ceramic particles as a dispersion phase in the matrix. The quantity ratio of the Si matrix occupying in the composite structure is 30 to 80%. The high-creep strength is maintained and creep deformation resistance is high even in a high temp. region exceeding about 1200 deg.C. The tube has the excellent oxidation resistance, etc., and is less oxidized and damaged by burner flames. The tube is formed thinner and lighter for its high creep strength and low density. The control of the furnace temp. with good accuracy is also possible as the effect of drastically decreasing the heat capacity of the tube.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite ceramic tube which is useful as a radiant tube or the like, has high creep strength, is excellent in oxidation resistance, melting resistance, thermal shock resistance and has a low heat capacity.

[0002]

2. Description of the Related Art Conventionally, 20Ni-25Cr has been used as a radiant tube material arranged in an annealing furnace for steel materials.
-Fe (ASTM standard HK40, JIS G5122
SCH22), 35Ni-25Cr-Fe (HP45,
SCH24), or 50Ni-30Cr-13W-
High Ni-high Cr alloy steels such as Fe have been used. Recently, the application of fine ceramics has been tried, for example, S
io ₂ or SiO ₂ —SiC composite ceramic fired product (Japan Iron and Steel Institute, “Iron and Steel” 69 (13) p. 11)
0,1983) and mullite (3Al ₂ O ₃ · 2SiO).
₂₎ -Al ₂ O ₃ -CaO based composite ceramics (Japanese Patent Laid-Open 2-9746 JP) proposes such have also been made.

[0003]

The radiant tube made of heat-resistant alloy steel is apt to be deformed by creep due to its own weight, thermal stress, and the like, and cracks due to the deformation during actual use. This is particularly noticeable on the burner side, and oxidation / melting damage of the tube wall due to contact with the burner flame also has a great effect on the tube life. Therefore, in actual operation, the heating temperature is about 10
Although it is used by limiting the temperature to 00 ° C or less, its useful life is only about 2 to 3 years, and it is not possible to cope with the recent demand for high temperature operation for the purpose of improving furnace operation efficiency. Attempts to apply ceramics are intended to meet the above requirements by enhancing high-temperature creep strength and heat resistance / melting resistance.
In order to apply ceramics to a radiant tube, it is necessary to satisfy not only high creep strength, oxidation resistance and melting resistance, but also resistance to cracking and spalling during heating and cooling processes. INDUSTRIAL APPLICABILITY The present invention provides a composite ceramic tube which has such various characteristics, can be stably used even at a high temperature operation exceeding about 1200 ° C., and can meet the demand for improvement in accuracy of furnace temperature control. It is provided.

[0004]

The composite ceramic tube of the present invention has a composite structure in which SiC ceramic particles are dispersed in matrix Si, and the amount ratio (volume ratio) of the matrix Si / SiC particles in the composite structure is Thirty
It is characterized by being / 70-80 / 20.

[0005]

The tube of the present invention has a high creep strength, a high creep deformation resistance, an oxidation resistance and a melt damage resistance even in a high temperature range of about 1200 ° C. or higher as a combined effect of Si-SiC. Have In addition, it has excellent thermal shock characteristics, and has crack resistance and spalling resistance against rapid heat and rapid cooling. Furthermore, due to its high creep strength, the wall thickness of the pipe wall (heat-resistant alloy steel tube has a wall thickness of approximately 10
(about mm) can be made thin and lightweight to about 3 mm. Moreover, its density (apparent density) is about 2.79, and that of heat-resistant alloy steel (about 7.85) is, of course,
Apparent density of other ceramics (eg, mullite: 3.
1, Sialon: smaller than 3.3). This thin wall
The reduction in weight is effective not only for mitigating the creep deformation due to its own weight when the tube is used at high temperatures, but also for improving the accuracy of furnace temperature control as the effect of reducing the heat capacity of the tube.

The present invention will be described in detail below. The composite ceramic tube of the present invention having a composite structure in which SiC ceramic particles are dispersed in the matrix Si has excellent creep strength as a SiC particle dispersion strengthening effect and high creep deformation resistance. Further, since the matrix is Si, SiO ₂ or Al ₂ O ₃
It has higher thermal shock characteristics than other fine ceramics, and has excellent cracking resistance and spalling resistance against rapid heating and quenching. Matrix Si in complex organization
Of SiC particles which are dispersed phase particles and "Matrix S
"i / SiC particles" (volume ratio) is set to 30/70 or more because if it is less than that, thermal shock and mechanical shock properties are not sufficient, especially crack resistance and spalling resistance against rapid heating and rapid cooling. On the other hand, the upper limit is set to 80/20 because if it exceeds that, the effect of strengthening the dispersion of the SiC particles becomes insufficient and it becomes difficult to secure high creep strength. The SiC particles as the dispersed phase particles may have a particle size of about 100 to 400 μm.

The composite ceramic tube of the present invention is S
i powder and SiC powder are used as raw materials, which are loaded into an induction heating furnace, and so-called zone heating melting (zone melting)
The method can be applied to manufacture. This will be described with reference to FIG. 1. 10 is a vertical induction heating furnace having a cylindrical shape, and 20 is an induction coil. The induction heating furnace 10
There is a space defined by the concentric cylindrical standing wall 11 and the cylindrical standing wall 12, and the Si powder P ₁ and the SiC powder P ₂ are filled in two concentric layers along the cylindrical standing wall. This powder filling operation is performed by causing each powder to flow into the space S from the hopper via the cylindrical feeder head.

As shown in the figure, Si powder P ₁ and SiC powder P ₂
And the inside of the furnace is maintained in an inert atmosphere or vacuum, and the powder in the furnace is heated by the induction coil 20 to melt the Si powder P ₁ . The melted Si penetrates into the particle gaps of the SiC powder P ₂ . This heating and melting operation is performed by the induction coil 20.
Is gradually lowered from the upper part of the furnace 10 (for example, 20 m
m / min). With the movement of the induction coil 20, the melting of the Si powder and the infiltration and solidification of the melted Si into the SiC particle gaps gradually progress from the top to the bottom to form a solidified body (tube) having a composite structure. It The composite ceramic tube of the present invention can be manufactured as a sintered product using a known sintering process, but the above method is extremely economical without requiring complicated equipment and operation. Moreover, according to this method, the specific gravity of Si powder and SiC powder (Si: 2.33, SiC:
A homogeneous and highly dense composite structure can be formed without accompanying unevenness of both components due to the difference of 3.17).

[0009]

【Example】

[1] Test Material As shown in FIG. 1, Si powder P ₁ was placed in a vertical induction heating furnace.
(Average particle size: 10 μm) and SiC powder P ₂ (Average particle size:
300 μm) in a two-layer concentric circle shape and subjected to high-frequency induction heating to dissolve the Si powder and infiltrate into the SiC powder particles, thereby having a composite structure in which the SiC particles are uniformly dispersed and mixed in the Si matrix. A tube was obtained.
This tube is referred to as a test material A. Tube size (mm): outer diameter 80, wall thickness 3, length 1200.

As comparative examples, the following test tubes B and C were prepared. Specimen B: 0.4C-20Ni-25Cr-Fe heat resistant alloy steel (ASTM standard HK40 material) tube (centrifugal casting tube: outer diameter 110 mm, wall thickness 10 mm), specimen C: 0.5C- 50Ni-30Cr-13W-F
e heat-resistant alloy steel tube (centrifugal casting tube: outer diameter 110
mm, wall thickness 10 mm).

The measurement results of various characteristics of the respective test materials A, B and C were measured and the results shown in Table 1 were obtained. (1) High temperature creep rupture test According to JIS Z2272. However, test temperature: 1
250 ° C., load: 0.5 Kg / mm ² . (2) High Temperature Oxidation Test A test piece is held in a heating furnace (atmosphere atmosphere) set at a temperature of 1250 ° C. for 100 hours to measure the oxidation weight loss. (3) Thermal shock test Test a: Immersion in water and rapid cooling to determine the maximum heating temperature at which cracking does not occur. Test b: A tube was heated to 1250 ° C by a burner (heating rate 1000 ° C / Hr), and then cooled to 600 ° C (cooling rate 1000 ° C / Hr). Repeated rapid heating / quenching operation, and cracking occurred. Find the number of iterations up to.

[0012]

[Table 1]

As shown in Table 1, test material A (invention example)
Has significantly better creep strength than the conventional radiant tubes made of heat-resistant alloy steel (test materials B and C),
High creep deformation resistance. Moreover, since it has a low coefficient of thermal expansion, deformation due to thermal stress is small. Its oxidation resistance is also high,
Excellent resistance to oxidative damage due to burner flame contact. Also, as a result of the high creep strength and the low density, the weight can be reduced significantly (about 1/3 or less), and therefore the specific heat is heat resistant. The heat capacity of the tube can be reduced while being about twice the size of alloy steel.

[0014]

The composite ceramic tube of the present invention is
Since it has excellent high-temperature creep strength, oxidation resistance, and melting resistance, even when it is used as a radiant tube as the burner-side tubing, creep deformation does not easily occur, and even when the burner flame is locally heated, it does not heat. It is less deformed by stress and has excellent resistance to melting loss and oxidation. Due to this improved material properties, temperatures around 1200 ° C
The above high temperature operation becomes possible, and effects such as improvement of service life, reduction of maintenance and improvement of furnace operation efficiency can be obtained.
Further, the composite ceramic tube of the present invention has a high creep strength, a low density and a light weight, so that the wall wall can be made thin (about 1/3 or less of the heat-resistant alloy steel tube), As a result, the heat capacity of the tube is reduced, and the effect of improving the accuracy of furnace temperature control can be obtained. Applications of the heat-resistant alloy steel of the present invention are not limited to those exemplified above, for example, a skid pipe that is a hearth constituent member of a steel material heat treatment furnace,
It is also useful as a material for hearth rolls and the like.

[Brief description of drawings]

FIG. 1 is a sectional explanatory view showing an example of a method for manufacturing a composite ceramic tube of the present invention.

[Explanation of symbols]

10: induction heating furnace, 20: induction heating coil, P ₁ : Si
Powder, P ₂ : SiC powder.

Claims (1)

[Claims] 1. A matrix Si having a composite structure in which SiC ceramic particles are dispersed in the matrix Si.
/ SiC particle amount ratio (volume ratio) is 30/70 to 80/2
A composite ceramic tube characterized by being 0.